[David M]

While underway, the Steaming ensign is flown from the mast. While not underway, the Holiday ensign is flown at the transom. The ensign is the flag of the country in which the vessel is documented. You "shift ensign" when you go from being underway to not underway.

The courtesy flag is a flag of the country in which the vessel is visiting. It is supposed to be flown from the mast on the starboard side if possible. Flying this flag earns brownie points with the locals and customs.